1. Field of the Invention
This invention relates to an apparatus for measuring the torque value and rotating speed of revolving machines such as engines and motors. More particularly, it concerns an apparatus for continuously measuring instantaneous values of the torque and rotating speed through real time calculation of them for each period of a pair of AC voltage signals received from an ordinary torque detector comprising a pair of gears secured to the shaft of a revolving machine at a distance from each other and electromagnetic pick-ups each disposed to face each of the gears.
2. Description of the Prior Art
The construction and operation of the conventional torque detecting apparatus will be described with reference to the accompanying drawing, in which FIG. 1 shows a schematic view of an ordinary torque detector mounted on a rotative shaft. FIG. 2 is a block diagram of a prior-art apparatus for measuring the instantaneous values of torque and rpm, and FIG. 3 is a waveform chart composed of a series of graphs of electrical wave shapes showing outputs of circuits shown in FIG. 2 for illustrating and assisting in the explanation of the operation of the apparatus of FIG. 2.
The apparatus of the prior art comprises a pair of gears 2, 3 mounted on a rotating shaft 1 at a suitable distance from each other and a pair of electromagnetic pick-ups or detectors 4 and 5 each disposed to face the tooth top of each of the gears 2 and 3.
With rotation of the shaft 1 the gears 2 and 3 are also rotated in unison, and AC voltage signals periodically varying according to the tooth form of the gears 2 and 3 are produced from the electro-magnetic pick-ups 4 and 5.
The frequency of the AC voltage signals is determined by the rotating speed on the shaft 1 and the number of teeth of the gears 2 and 3. In general, the gears 2 and 3 have the same number of teeth, so that the AC voltage signals produced from the electromagnetic pick-ups 4 and 5 have the same frequency.
Meanwhile, when torque is applied to the shaft 1, the shaft 1 is twisted in proportion to the torque, and as a result the gears 2 and 3 are displaced in the peripheral directions in proportion to the angle of twist in the shaft portion with the gears 2 and 3 mounted thereon.
Thus, the timing of generation of AC voltage signals produced from the electromagnetic pick-ups 4 and 5 is changed in proportion to the displacement of the gears 2 and 3 in the peripheral direction. Consequently, a phase difference proportional to the angle of twist of the shaft portion 1 between the gears 2 and 3 is provided between the two AC voltage signals.
As is shown, the pair of AC voltage signals produced from the usual torque detector has a phase difference proportional to the torque and a frequency proportional to the rotating speed of the shaft, and they are transmitted to a measuring apparatus for measuring the instantaneous values of torque and rotating speed.
The terms "instantaneous value of torque" and "instantaneous value of rotating speed" are accurately defined here respectively as average torque and average rotating speed within a time interval required for the rotation of the shaft 1 for one pitch of the teeth of the gears 2 and 3, that is, within the period of the AC voltage signals, measured for each period. However, assuming the number of teeth to be, for instance, 60, the averaging period is very short, namely 0.0002 sec. at 5,000 rpm and 0.0001 sec. at 10,000 rpm, so that the average value can be regarded to be the instantaneous value.
FIG. 2 shows a measuring apparatus for measuring the instantaneous values of torque and rotating speed from a pair of AC voltage signals taken out from the usual torque detector shown in FIG. 1.
In FIG. 2, designated at 4 and 5 are the aforementioned pick-ups, and the AC voltage signals therefrom are transmitted to respective voltage comparators 10 and 11 for comparison with zero potential. These voltage comparators each provide a pulse every time the AC voltage signal comes to coincidence with zero potential as it changes from the negative potential to the positive potential. The pulse outputs of the voltage detectors 10 and 11 are pulse series signals as shown at 10 and 11 in FIG. 3 comprising pulses each produced for each period of the period of the AC voltage signals. Designated at 12 is a gate control circuit, to which the pulses of the voltage comparators 10 and 11 are transmitted as gate control signal, and which produces a gate signal which becomes "on" when the pulse series signal from the voltage comparator 10 leading in the timing of generation is transmitted and "off" when the pulse series signal from the other voltage comparator 11 is transmitted. Thus, the time interval of the "on" state of the gate signal is equal to the difference of the timing of generation between the two voltage signals.
Designated at 13 is an AND circuit, and at 14 a clock pulse generator. The AND circuit 13 receives the gate signal from the gate control circuit 12 and clock pulses from the clock pulse generator 14 and passes clock pulses only for the time interval of the "on" state of the gate signal. Thus, the output of the AND circuit 13 is a pulse signal group, in which clock pulses are present only for a time interval corresponding to the difference of the timing of generation between the two AC voltage signals.
Designated at 15 is a data recorder for recording the pulse group signal produced from the AND circuit 13.
By the above prior-art apparatus, the instantaneous values of torque and rotating speed are calculated from the recorded pulse signal. However, it has to be noted that the number of pulses in each pulse group which numbers are counted while the pulse group signal is recorded in the data recorder 15, is not proportional to the instantaneous torque.
This is because along with doubling of the rotating speed of the shaft 1, the frequency of the AC voltage signals is also doubled, and consequently the difference T" (T".sub.1, T".sub.2, . . . ) of the timing of generation between the two AC voltage signals is reduced to one half. Thus, the number of pulses in each pulse group is reduced to one half even if the phase difference (owing to torque) is the same. Accordingly, it has hitherto been in practice to once record the pulse group signal in a data recorder 15 and then reproduce it and transmit it to a computer for counting the number of pulses in each pulse group proportional to the difference T" of the timing of generation between the two AC voltage signals while also measuring the period for each pulse group which is equal to the period T of the AC voltage signals to determine the instantaneous torque value through calculation of the ratio T"/T proportional to the phase difference between the AC voltage signals and also determine the instantaneous rotating speed value through calculation of the inverse value 1/T of the period T of the pulse group.
In this case, with the computer it is difficult to make the above calculation for each period T since the calculation required time. Therefore, it has been in practice to progressively measure and memorize the number of pulses in each pulse group and the period between adjacent pulse groups of pulse group signals introduced from the data recorder 15 and make the above calculation.
As has been shown, in the prior art in order to obtain the instantaneous values of torque and rotating speed it has been necessary to once record data and then reproduce them for calculation. Therefore, a great deal of time delay is involved until the instantaneous values of torque and rotating speed are obtained, so that the results of measurement cannot be obtained on a real time basis.
In order to resolve this shortcoming there have been attempts to attach a strain gauge to the shaft 1 and convert the strain of the shaft in proportion to the torque to the corresponding voltage signal. However, the apparatus used to this end requires a slip ring for taking out the signal, so that it provides problems in its durability. In addition, since the signals are treated analogwise, the precision in the strain gauge system is inferior to the first mentioned apparatus.